[R] By() with method = spearman

[Chuck Cleland]

Doran, Harold wrote:
> I have a data set where I want the correlations between 2 variables
> conditional on a students grade level.
> 
> This code works just fine.
> 
> by(tmp[,c('mtsc07', 'DCBASmathscoreSPRING')], tmp$Grade, cor,
> use='complete', method='pearson')
> 
> However, this generates an error
> 
> by(tmp[,c('mtsc07', 'DCBASmathscoreSPRING')], tmp$Grade, cor,
> use='complete', method='spearman')
> Error in FUN(data[x, ], ...) : 'x' is empty
> 
> I can subset the data by grade and compute spearman rho as
> 
> tmp5 <- subset(tmp, Grade == 5)
> cor(tmp5[,c('mtsc07', 'DCBASmathcountSPRING')], use='complete',
> method='spearman')
> 
> But doing this iteratively is inefficient.
> 
> I don't see anything in the help man for by() or cor() that tells me
> what the problem is. I might be missing it though. Any thoughts?

  It works as expected using the iris data:

by(iris[,c('Sepal.Length', 'Sepal.Width')], iris$Species, cor,
   use='complete', method='spearman')

iris$Species: setosa
             Sepal.Length Sepal.Width
Sepal.Length    1.0000000   0.7553375
Sepal.Width     0.7553375   1.0000000
---------------------------------------------------------------------------------------------------------------------

iris$Species: versicolor
             Sepal.Length Sepal.Width
Sepal.Length     1.000000    0.517606
Sepal.Width      0.517606    1.000000
---------------------------------------------------------------------------------------------------------------------

iris$Species: virginica
             Sepal.Length Sepal.Width
Sepal.Length    1.0000000   0.4265165
Sepal.Width     0.4265165   1.0000000

> sessionInfo()
R version 2.5.1 Patched (2007-09-16 r42884)
i386-pc-mingw32

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] "stats"     "graphics"  "grDevices" "utils"     "datasets"
"methods"   "base"

other attached packages:
 lattice
"0.16-5"

> Thanks,
> Harold
> 
> 
>> sessionInfo()
> R version 2.5.0 (2007-04-23) 
> i386-pc-mingw32 
> 
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
> States.1252;LC_MONETARY=English_United
> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
> 
> attached base packages:
> [1] "stats"     "graphics"  "grDevices" "utils"     "datasets"
> "methods"   "base"     
> 
> other attached packages:
>  lattice 
> "0.15-4" 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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> and provide commented, minimal, self-contained, reproducible code. 

-- 
Chuck Cleland, Ph.D.
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